Recycling of plastics in a steam cracker

ABSTRACT

A process for recycling plastic waste in a steam cracker, wherein a melt obtained from plastic waste is converted into products at from 400° 550° C., and a distillate fraction is separated off from the products at from 180° to 280° C. and is fed as feed material to a steam cracker.

This application is a 371 of PCT/EP94/01647 filed on Sep. 20, 1994.

The present invention relates to a process for recycling plastics in asteam cracker.

It is possible by means of the process according to the invention toconvert plastics, for example pure polymeric plastic waste, mixedplastic waste or sheet waste, including possible soiling, sticky labelmaterials, fillers, residual contents etc., into high-value feedmaterials for the known steam cracking process. These feed materials arein turn converted in the known steam cracking process, into crackedproducts such as ethylene, propylene, C₄ mixtures, pyrolysis gasolineetc., and these are produced in yields which are almost the same as oreven higher than when the steam cracker is operated with the traditionalfeed materials such as naphtha, liquid petroleum gas (LPG) and gas oil.It is therefore possible by means of the process according to theinvention to replace in the steam cracking process the abovementionedtraditional feed materials by feed materials obtained from plasticwaste, it being unnecessary to admix naphtha, LPG or gas oil with thefeed materials obtained from plastic waste.

The process according to the invention therefore makes a considerablecontribution to the economic recycling of plastics.

The known steam cracking process is usually understood as evaporationand heating of the feed materials at up to 650° C. with subsequenttreatment at in general from 700° to 1100° C., for example from 780° to860° C., in the course of, usually, from 0.02 to 10, for example from0.1 to 2, seconds in the presence of steam.

It is known that the plastic wastes obtained as garbage consist of about70% by weight of polyolefins, such as polyethylene and polypropylene,about 15% by weight of styrene polymers, about 10% by weight of PVC andminor amounts of about 5% by weight of other plastics, such aspolyurethane, polyester and polyamide. These plastic wastes aregenerally soiled, ie. they also contain sticky label materials, fillers,residual contents, etc. The plastic wastes are usually sorted and aretherefore obtained in various fractions known per se. The bottle or blowmolded fraction composed of bottles, containers, etc., which essentiallyconsist of polyolefins, such as polyethylene or polypropylene, a mixedplastic fraction, consisting essentially of polyethelene (PE),polypropylene (PP), styrene polymer, such as polystyrene (PS), andpolyvinyl chloride (PVC); a sheet fraction consisting essentially of PEand PP, etc., and a light fraction consisting essentially of PE, PP andPS, in each case possibly with adherent soiling, sticky label materials,fillers, residual contents, etc., may be mentioned. Essentially, thefractions contain plastics other than the stated ones only in minoramounts, for example less than 10% by weight, in many cases less than 5%by weight, in particular less than 2% by weight.

A number of processes have been described in the patent literature forconverting plastic waste into products for further processing, forexample catalytic or thermal processes, hydrocracking processes,extrusion processes etc. For example, Europ. Patent Application 0 502618 describes a process in which plastic waste, specificallypolyolefins, is converted into lower hydrocarbons. This entails theplastic waste being reacted in a fluidized bed apparatus at about300°-630° C. The resulting lower hydrocarbons, such as paraffins orwaxes, can be converted by means of the known steam cracking processinto olefins. Plastic waste can be converted by the combination offluidized bed apparatus and known steam cracking process into theseolefins.

An evident disadvantage of this process is that for the steam crackingprocess it is necessary to add naphtha to the feed materials obtained,ie. it is not possible to convert the plastic waste into crackedproducts such as ethylene, propylene etc. without adding traditionalfeed materials. Furthermore, the handling of the solids in the fluidizedbed always proves to be a disadvantage. It is also problematic to scaleup a process of this type to large-scale industrial operation.

Patent Application WO 93/18112 published on Sep. 16, 1993, describes aprocess for the preparation of olefins from plastic waste byestablishing a desired viscosity by thermal pretreatment of the plasticwaste at from 380° to 680° C. and subsequent thermal treatment of theproduct at from 700° to 1100° C. The process does not involve anydistillative separation of the product. The process cannot produce aproduct which can be evaporated without leaving a residue.

It is an object of the present invention to provide a process which canbe used industrially on a large scale and with which plastic waste isconverted into high-value feed materials for a steam cracker which maybe available, so that these feed materials can be converted, without theaddition of, for example, naphtha, LPG and gas oil, in the steamcracking process into cracked products such as ethylene, propylene, C₄mixtures and pyrolysis gasoline in high yield.

We have found that this object is achieved if a melt obtained fromplastic waste is converted into products at from 400° to 550° C., adistillate fraction being separated off from the products at from 180°to 280° C., preferably from 220° to 260° C., in particular from 230° to250° C., and said fraction is fed as a feed material to a steam cracker.

In an advantageous embodiment of the process,

the plastic waste is melted, in general at from 280° to 380° C.,

the melt is fed to a reactor where the polymers are converted at from400° to 550° C. into products which can be evaporated and cracked in aconventional way in the steam cracker,

a distillate fraction is separated by distillation, at from 200° to 280°C., preferably from 220° to 260° C., in particular from 230° to 250° C.,from the products,

the other products are returned to the reactor, with the exception ofresidues and solids and any inorganic acids and possibly aromatics, and

the distillate fraction separated off is introduced, if necessary afterfurther separation, as a feed material into the steam cracker.

In some cases, it has proven advantageous to separate off aromatics,such as ethyl benzene and styrene, from the distillate fraction beforeit is used in the steam cracker. This can be done by known methods, suchas extraction or distillation. The aromatics can then be usedseparately, for example added directly to the aromatics fraction(pyrolysis gasoline) of the products of the steam cracker.

The process is advantageously used for blow molded fractions and sheetfractions. Melting of the plastic waste is preferably carried out atfrom 280° to 350° C., in some cases at from 300° to 350° C., inparticular from 290° to 320°, and the conversion in the reactor at from400° to 450° C.

The distillate fraction or fractions is or are preferably separated offby a process in which

the products are separated by means of a 1st column which is directlydownstream of the tubular furnace into

a bottom product resulting at from 300° to 420° C., in particular from330° to 380° C., which, after removal of the residues and solids, isreturned to the reactor, and into

a top product resulting at from 200° to 280°, preferably from 220° to260°C., in particular from 230° to 250° C., which, after partialcondensation, is fed into a 2nd column at 70° to 150° C., in particularfrom 100° to 120° C.,

the liquid/gas mixture resulting after the partial condensation isseparated by means of the above 2nd column into

a liquid mixture emerging, in general at from 50° to 100° C., at thebottom of the 2nd column, which is, on the one hand, returned to the 1stcolumn and, on the other hand, used as feed material for the steamcracker, and into

a gas mixture emerging, in general, at from 20° to 80° C., at the top ofthe 2nd column, which is used as feed material for the steam cracker.

If the plastic waste contains significant amounts, ie. usually more than5% by weight, of chlorine-containing plastic, such as polyvinylchloride, and/or aromatics-containing plastic, such as styrene polymer,as, for example, in a mixed plastic fraction, it has proven advantageousto melt the plastic waste at from 330° to 380° C., in particular from320° to 350° C., the polyvinyl chloride simultaneously beingdehydrohalogenated, and to carry out the conversion into products in thereactor at from 410° to 530° C., preferably from 420° to 480° C., inparticular from 430° to 480° C. Said products can be evaporated andcracked in a conventional way in the steam cracker.

For the dehydrohalogenation, a residence time of from 1 hour to 20 hoursis generally sufficient at the temperatures used. The time requireddepends on the desired degree of dehydrohalogenation and can be readilydetermined by a person skilled in the art by means of simple preliminaryexperiments. In some cases, particularly when the dehydrohalogenation iscontinued after the melting, for example at from 250° to 300° C., thedesired residence time may be up to about 5 days. This canadvantageously take place during temporary storage.

The distillate fraction is preferably separated off by a process inwhich

the products are separated by means of a 1st column which is directlydownstream of the reactor into

a bottom product resulting at from 330° to 450° C., in particular from350° to 400° C., which, after removal of the residues and solids, isreturned to the reactor, and into

a top product resulting at from 200° to 280° C., in particular from 230°to 250° C., which, after partial condensation, is fed to a 2nd column atfrom 70° to 150° C., in particular from 100° to 120° C.,

the liquid/gas mixture resulting after the partial condensation isseparated by means of the above 2nd column into

a liquid mixture emerging, in general at from 50° to 100° C., at thebottom of the 2nd column, which is, on the one hand, returned to the 1stcolumn and, on the other hand, fed to a distillation or extraction unitsuitable for removing aromatics, and into

a gas mixture emerging, in general at from 20° to 80° C., at the top ofthe 2nd column, which is used as feed material for the steam cracker.

The liquid mixture fed to the above distillation or extraction unit isin general separated into

a liquid fraction which is used as feed material for the steam cracker,and into

an aromatic fraction.

The heat of condensation of the top product from the first column can beused for generating steam at various pressures.

The plastic waste can be melted in suitable apparatuses which ensuresufficient heat transfer and the required thorough mixing. The stirredcontainer, such as stirred kettles or in particular intensively stirredkettles, which can be equipped with a heating jacket and/or internalheater has proven useful. The melting process is usually relativelyrapid, ie. complete after from 0.5 to 30 minutes. Advantageously, forexample, when dehydrohalogenation is being carried out, a plurality ofthese stirred containers, for example two or three, are operated in acascade.

Conventional apparatuses, such as stirred containers or extruders, maybe used as the reactor for converting the melt into products. A tubularfurnace is advantageous. In many cases, it has proven advantageous ifsome of the reaction products leaving the tubular furnace are recycledto the tubular furnace to increase the residence time. In thisprocedure, the conversion to the products takes place partly in therecycle pipe used for this purpose, if necessary in a delay tank,depending on the temperature and residence time conditions. The tubularfurnace is in general a heat exchanger in which heat is transferred fromthe gas phase present outside the pipes into the material, for examplethe melt, present in the pipes. A reformer, a coker, a refinery furnaceor in particular a tubular cracker, as used, for example, in steamcrackers, may advantageously be employed (cf. for example UlmannsEncyklopadie der technischen Chemie, 4th edition, Volume 3, page 476 andpages 330/331).

The conversion into the products is advantageously carried out in theabsence of air, for example under nitrogen, so that oxidation during thepyrolysis is avoided.

For the purposes of the present invention, residues and solids arematerials which remain behind in the distillative separation and do notboil below 500° C., if they boil at all. These are, for example,impurities adhering to the plastic waste, paper residues, cokingproducts, glass and metal residues, sand, pigment residues, fillers orthe like.

In the novel process, it has proven advantageous to pass at least someof the bottom product of the first column as a heating medium throughthe heating jacket of the melting container before it is returned to thereactor. The average residence time in the reactor is usually from 0.05to 10 hours.

The normal process is generally carried out at from 0.8 to 2.0 bar,preferably at atmospheric pressure, ie. 1 bar. The stated boiling pointor boiling ranges are based on 1 bar.

The plastic waste can be used with or without drying. Depending on thedimensions of the melting unit and its feed apparatuses, it may benecessary to comminute the plastic waste by generally known methods,such as shredding or milling. Good results are obtained with averageparticle sizes of from 2 to 10 mm. Particle sizes of from 1 to 10 cm andin some cases also uncomminuted plastic waste are also suitable.

The dependent claims relate to other features of the process accordingto the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scematic drawing of the simplified process for carrying outthe present invention.

FIG. 2 is a simlified drawing which includes a modification of theprocess of FIG. 1.

The process according to the invention is described in detailhereinafter for the example shown in the simplified process diagram inFIG. 1.

Dry and comminuted plastic waste 2, for example a blow molded fraction,is fed via a conveyor 1, eg. a conveying screw, from a storage container3 into a stirring container 4 which is equipped with a heating jacket.In this stirring container the plastic waste is converted at about 300°C. into an easily pumped melt. During this a dehydrohalogenation maytake place if some PVC has inadvertently slipped through the sorting ofthe plastic waste. Any HCl 5 which is produced is converted with waterby known processes, which are not relevant to the invention, intoaqueous HCl which can be fed to other production processes orneutralized with NaOH. The above melt is fed by means of a forcedcirculation pump to a steam cracker 6 (called the cracker hereinafter).In this cracker the polymers are converted, without the addition ofhydrogen, vapor, catalysts, solvents or diluents, into products whichcan be vaporized and cracked in the steam cracker in a conventional way.This involves at about 420° C. a thermal liquid cracking and,furthermore, any remaining dehydrohalogenation takes place in thecracker. The required heat is supplied from outside, for example by oilor gas heating. The liquid/vapor mixture leaving the cracker is feddirectly to a column 7, for example an enriching column. The bottomproduct removed at about 350° C. comprises the higher boiling productswhich have not been converted into short-chain hydrocarbons. This is, onthe one hand, returned directly to the cracker and, on the other hand,passed as heat-transfer agent through the melt in the stirring containerand through the heating jacket of the stirring container and finallyreturned to the cracker. Residues and solids 8 are removed, for exampleby means of a hydrocyclone 9, from the bottom product after it has leftthe column. The vapor mixture leaving the top of the column at about240° C. is fed, after a partial condensation, to another column 10, forexample a packed column, at about 110° C. The liquid/gas mixtureentering the packed column is washed with water or aqueous NaOH 11 incountercurrent; any HCl still present in the gas is removed as aqueousHCl or aqueous NaCl solution with the liquid mixture at the bottom. Theliquid mixture emerging at the bottom (organic liquid/aqueous HCl oraqueous NaCl solution) is separated in a downstream phase separatingvessel 12. The lighter organic phase is, on the one hand, removed fromthe process as feed material A for the steam cracker and, on the otherhand, returned to the column. The heavier aqueous phase, possiblyenriched with HCl or NaCl 13, is removed from the process. The HCl-freegas mixture emerging at the top of the packed column is likewise fed tothe steam cracker as feed material B.

Furthermore, FIG. 2 shows byway of example the simplified processdiagram for a mixed plastic fraction: comminuted, dried plastic waste 2,for example a mixed plastic fraction, is fed via a conveyor 1, forexample a conveying screw, from a storage container 3 to a stirringcontainer 4 which is equipped with a heating jacket. In this stirringcontainer the plastic waste is converted at about 350° C. into an easilypumped melt. During this, dehydrohalogenation to the extent of 98-99% ofthe chlorine content in the PVC takes place. The resulting HCl 5 isconverted by water by known processes which are not relevant to theinvention into aqueous HCl which can be fed to other productionprocesses or neutralized with NaOH. The melt is fed by means of a forcedcirculation pump into a cracker 6. In this cracker the polymers areconverted, without the addition of hydrogen, vapor, catalysts, solventsor diluents, into products which can be evaporated and cracked in thesteam cracker in a conventional way. This involves at about 450° C. athermal liquid cracking and, furthermore, the remainingdehydrohalogenation takes place in the cracker. The required heat issupplied from outside, for example by oil or gas heating. Theliquid/vapor mixture leaving the cracker is directly fed to a column 7,for example an enriching column. The bottom product removed at about380° C. comprises the higher boiling products which have not beenconverted into short-chain hydrocarbons. This is, on the one hand,directly returned to the cracker and, on the other hand, passed asheat-transfer agent through the melt in the stirring container andthrough the heating jacket of the stirring container and finallyreturned to the cracker. Residues and solids 8 are removed from thebottom product after it has left the column, for example by means of ahydrocyclone 9. The vapor mixture emerging at the top of the column atabout 240° C. is, after a partial condensation, fed to another column10, for example a packed column, at about 110° C. The liquid/gas mixtureentering the packed column is washed with water or aqueous NaOH 11 incountercurrent; the HCl contained in the gas is removed as aqueous HClor aqueous NaCl solution with the liquid mixture at the bottom. Theliquid mixture emerging at the bottom (organic liquid/aqueous HCl oraqueous NaCl solution) is separated in a downstream phase separationvessel 12. The lighter organic phase (see Table 11) is, on the one hand,fed to a distillation or extraction unit 20 suitable for removingaromatics, and, on the other hand, returned to the column. The heavieraqueous phase, enriched in HCl or NaCl 13, is removed from the process.The HCl-free gas mixture emerging at the top of the packed column is fedas feed material D to the steam cracker. The organic liquid fed to theabove distillation or extraction unit is separated, on the one hand,into the feed material C for the steam cracker and, on the other hand,into an aromatic fraction X in a column 20; both fractions are removedfrom the process.

It is self-evident that modification of the features of the processwhich have been indicated by a skilled worker within the scope ofconventional technology does not change the fundamental inventiveness.

The feed materials obtained can be evaporated and cracked in theconventional way in the steam cracker.

The novel process has, inter alia, the advantage that, when thesafecracker is operated with the desired product obtained from theplastic waste, heat energy can be saved compared with naphtha as thefeed material. It manages without the addition of hydrogen, diluents orsolvents and operates virtually at atmospheric pressure. Furthermore,the process has the advantage that the steam cracker is supplied withfeed materials which can be evaporated without leaving a residue.

In some cases, it has proven advantageous to produce synthesis gas fromthe removed residues and solids 8 by conventional gasification by aknown process, such as the Shell or Texaco process (eg. UllmannsEncyklopadie der technischen Chemie, 4th edition, Volume 14, pages 395to 397), for example in a cyclone gasifier. The slag obtained can bedeposited in a landfill or used as building material.

The aromatics obtained from the distillation or extraction unit 20,which in itself is not relevant to the invention, can frequently befurther processed. These are in general a mixture of styrene, ethylbenzene, toluene and benzene as the main components. They can be used asraw material, for example in conventional plants for the conversion ofethyl benzene into styrene, as described in Ullmanns Encyklopadie dertechnischen Chemie, 4th edition, Volume 22, pages 293 to 309.Furthermore, after hydrogenation of the double bonds, they can be usedin aromatics plants in which essentially benzene is prepared from amixture of benzene, toluene and xylene (Ullmanns Encyklopadie dertechnischen Chemie, 4th edition, Volume 8, pages 383 to 411).

EXAMPLE 1

A blow molded fraction which is obtained from Duales System DeutschlandGmbH, Bonn, Germany, and whose plastic content essentially consists ofpolyethylene and polypropylene, including any adherent soiling, stickylabel materials, fillers, residual contents, etc., is processed in theplant of FIG. 1, described above. The resulting feed materials A (liquidmixture) and B (gas mixture) for the steam cracker have the compositionsshown in Tables 1 and 2.

The cracked products obtainable thereby from the steam cracking processhave the compositions shown in Tables 3 and 4. For comparison, thecompositions of the cracked products if the steam cracker is operatedwith the traditional feed material naphtha are shown in these last twotables. Comparison shows that the yield of ethylene and propylene ishigher if the steam cracker is operated with the feed materials obtainedfrom the blow molded fraction than if the steam cracker is operated withnaphtha. The results of the conversion of the blow molded fraction ofthe plastic waste are as follows:

    ______________________________________                                        organic liquid mixture =                                                                             =  74.0% by wt.                                        feed material A for steam cracker                                             HCl-free gas mixture = =  16.0% by wt.                                        feed material B for steam cracker                                             residues (organic high-boiling                                                                       =  2.5% by wt.                                         hydrocarbons)                                                                 solids (residues on ignition)                                                                        =  7.5% by wt.                                                                100.0% by wt.                                          and thus the organic content = 92.5% by weight.                               ______________________________________                                    

EXAMPLE 2

A mixed plastic fraction which is obtained from Duales SystemDeutschland GmbH, Bonn, and whose plastic content essentially consistsof polyethylene, polypropylene, styrene polymer and polyvinyl chloride,including any adherent soiling, sticky label materials, fillers,residual contents, etc., is processed in the plant of FIG. 2, describedabove. The resulting feed materials C (liquid mixture) and D (gasmixture) for the steam cracker have the compositions shown in Tables 12and 13.

The cracked products obtainable thereby from the steam cracking processhave the compositions as shown in Tables 14 and 15.

The results of the conversion of the mixed plastic fraction of theplastic waste were as follows.

    ______________________________________                                        organic liquid mixture =                                                                             =  34.2% by wt.                                        feed material C for steam cracker                                             HCl-free mixture =     =  21.8% by wt.                                        feed material D for steam cracker                                             aromatic fraction, mainly ethylbenzene                                                               =  25.8% by wt.                                        and styrene                                                                   residues (high-boiling hydrocarbons)                                                                 =  12.0% by wt.                                        solids (residues on ignition)                                                                        =  5.0% by wt.                                                                =  1.2% by wt.                                                                100.0% by wt.                                          and thus the organic content = 93.8% by weight.                               ______________________________________                                    

The following abbreviations are used in the tables hereinafter:HC=hydrocarbons, NA=non-aromatics, EB=ethylbenzene

                  TABLE 1                                                         ______________________________________                                        Blow molded fraction                                                          Feed material A = liquid mixture for the steam cracker,                       obtained from the process according to                                        the invention                                                                 Composition       % by wt.!                                                   ______________________________________                                        C.sub.3 HC       0.01                                                         1-butene         0.05                                                         other butenes    0.04                                                         n-butane         0.04                                                         1-pentene        0.20                                                         other pentenes   0.16                                                         i-pentane        0.01                                                         n-pentane        0.32                                                         further C.sub.6 HC                                                                             0.48                                                         methylcyclopentene                                                                             0.12                                                         1-hexene         1.79                                                         methylcyclopentane                                                                             0.07                                                         other hexenes    0.24                                                         n-hexane         1.08                                                         methylcyclohexene                                                                              0.84                                                         other C.sub.7 HC 0.86                                                         1-heptene        2.50                                                         methylcyclohexane                                                                              0.33                                                         n-heptane        2.34                                                         1-octene         2.59                                                         other C.sub.8 HC 2.59                                                         n-octane         2.63                                                         1-nonene         3.59                                                         other C.sub.9 HC 3.42                                                         n-nonane         3.02                                                         other C.sub.10 HC                                                                              1.40                                                         1-decene         3.96                                                         n-decane         3.34                                                         1-undecene       3.48                                                         other C.sub.11 HC                                                                              1.45                                                         n-undecane       2.88                                                         1-dodecene       3.45                                                         other C.sub.12 HC                                                                              1.75                                                         n-dodecane       3.41                                                         1-tridecene      3.56                                                         other C.sub.13 HC                                                                              2.04                                                         n-tridecane      3.73                                                         other C.sub.14 HC                                                                              2.16                                                         1-tetradecene    3.61                                                         n-tetradecane    3.64                                                         other C.sub.15 HC                                                                              1.45                                                         1-pentadecene    3.33                                                         n-pentadecane    3.58                                                         other C.sub.16 HC                                                                              1.23                                                         1-hexadecene     2.76                                                         n-hexadecane     3.58                                                         other C.sub.17 HC                                                                              0.73                                                         1-heptadecene    2.18                                                         n-heptadecane    3.43                                                         other C.sub.18 HC                                                                              0.17                                                         1-octadecene     1.24                                                         n-octadecane     3.07                                                         total            100.00                                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Blow molded fraction                                                          Feed material B = gas mixture for the steam cracker,                          obtained from the process according to                                        the invention                                                                 Composition       % by wt.!                                                   ______________________________________                                        H.sub.2          0.22                                                         CH.sub.4         3.65                                                         C.sub.2 H.sub.6  8.89                                                         C.sub.2 H.sub.4  2.76                                                         C.sub.3 H.sub.8  13.16                                                        C.sub.3 H.sub.6  13.78                                                        i-C.sub.4 H.sub.10                                                                             0.22                                                         n-C.sub.4 H.sub.10                                                                             9.31                                                         1-C.sub.4 H.sub.8                                                                              7.83                                                         i-C.sub.4 H.sub.8                                                                              3.14                                                         2-C.sub.4 H.sub.8 t                                                                            1.80                                                         2-C.sub.4 H.sub.8 c                                                                            1.31                                                         C.sub.4 H.sub.6  0.93                                                         i-C.sub.5 H.sub.12                                                                             0.47                                                         n-C.sub.5 H.sub.12                                                                             11.51                                                        C.sub.5 H.sub.10 10.60                                                        benzene          0.71                                                         C.sub.6 H.sub.12 9.71                                                         total            100.00                                                       ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Blow molded fraction                                                          Cracked product from the steam cracker                                        I) with feed material A from the process according to                         the invention                                                                 II) with naphtha as feed material                                                              % by wt.!                                                    Composition       I      II                                                   ______________________________________                                        CO                0.1    0.2                                                  H.sub.2           0.7    1.0                                                  CH.sub.4          10.7   14.6                                                 C.sub.2 H.sub.6   3.6    3.1                                                  C.sub.2 H.sub.4   33.1   29.9                                                 C.sub.2 H.sub.2   0.4    0.5                                                  C.sub.3 H .sub.8  0.4    0.4                                                  C.sub.3 H.sub.6   16.8   15.2                                                 propyne           0.2    0.3                                                  propadiene        0.3    0.4                                                  i-C.sub.4 H.sub.10                                                                              0.0    0.0                                                  n-C.sub.4 H.sub.10                                                                              0.1    0.2                                                  1-butene          2.1    1.4                                                  i-butene          0.7    2.1                                                  2-butene (c)      0.5    0.5                                                  2-butene (t)      0.4    0.3                                                  C.sub.4 H.sub.6   7.2    4.9                                                  C.sub.5 HC        5.2    4.5                                                  C.sub.6 -C.sub.8 NA                                                                             1.8    2.1                                                  benzene           7.8    7.9                                                  toluene           2.9    3.5                                                  EB + xylenes      0.6    1.1                                                  styrene           0.8    1.0                                                  C.sub.9 HC        0.7    0.9                                                  C.sub.10 + HC     3.0    4.0                                                  total             100.0  100.0                                                ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Blow molded fraction                                                          Cracked product (gas mixture) from the steam cracker                          I) with feed material B from the process according to                         the invention                                                                 II) with naphtha as feed material                                                              % by wt.!                                                    Composition       I      II                                                   ______________________________________                                        CO                0.2    0.2                                                  H.sub.2           1.0    1.0                                                  CH.sub.4          16.8   14.6                                                 C.sub.2 H.sub.6   6.5    3.1                                                  C.sub.2 H.sub.4   31.8   29.9                                                 C.sub.2 H.sub.2   0.7    0.5                                                  C.sub.3 H.sub.8   3.2    0.4                                                  C.sub.3 H.sub.6   16.1   15.2                                                 propyne           0.3    0.3                                                  propadiene        0.5    0.4                                                  i-C.sub.4 H.sub.10                                                                              0.0    0.0                                                  n-C.sub.4 H.sub.10                                                                              1.0    0.2                                                  1-butene          1.0    1.4                                                  i-butene          0.9    2.1                                                  2-butene (c)      0.4    0.5                                                  2-butene (t)      0.3    0.3                                                  C.sub.4 H.sub.6   4.9    4.9                                                  C.sub.5 HC        2.6    4.5                                                  C.sub.6 -C.sub.8 NA                                                                             0.5    2.1                                                  benzene           6.0    7.9                                                  toluene           1.7    3.5                                                  EB + xylenes      0.3    1.1                                                  styrene           0.6    1.0                                                  C.sub.9 HC        0.3    0.9                                                  C.sub.10 + HC     2.3    4.0                                                  total             100.0  100.0                                                ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Mixed plastic fraction                                                        Feed material for the distillation or extaction unit                          for removing the aromatic fraction, ob-                                       tained from the process according to the                                      invention                                                                     Composition       % by wt.!                                                   ______________________________________                                        C.sub.2 HC       <0.01                                                        C.sub.3 HC       0.14                                                         n-butane         0.05                                                         1-butene         0.21                                                         other butenes    0.05                                                         i-pentane        0.02                                                         n-pentane        1.45                                                         1-pentene        0.24                                                         other pentenes   0.36                                                         n-hexane         0.57                                                         1-hexene         2.22                                                         other hexenes    0.81                                                         methylcyclopentane                                                                             0.12                                                         methylcyclopentene                                                                             0.13                                                         other C.sub.6 HC 0.95                                                         benzene          2.93                                                         n-heptane        1.03                                                         1-heptene        1.15                                                         methylcyclohexane                                                                              0.09                                                         methylcyclohexene                                                                              0.94                                                         other C.sub.7 HC 1.42                                                         toluene          6.72                                                         n-octane         1.02                                                         1-octene         1.43                                                         ethylcyclohexane 5.56                                                         ethylbenzene     8.84                                                         para-xylene      0.27                                                         meta-xylene      0.20                                                         ortho-xylene     0.36                                                         styrene          9.64                                                         other C.sub.8 HC 1.37                                                         n-nonane         1.83                                                         1-nonene         1.45                                                         i-propylbenzene  1.58                                                         n-propylbenzene  0.40                                                         other C.sub.9 HC 4.43                                                         n-decane         1.92                                                         1-decene         1.60                                                         other C.sub.10 HC                                                                              1.65                                                         n-undecane       1.29                                                         1-undecene       1.36                                                         other C.sub.11 HC                                                                              3.43                                                         n-dodecane       1.41                                                         1-dodecene       1.34                                                         other C.sub.12 HC                                                                              3.93                                                         n-tridecane      1.46                                                         1-tridecene      1.53                                                         other C.sub.13 HC                                                                              4.05                                                         n-tetradecane    1.43                                                         1-tetradecene    1.31                                                         other C.sub.14 HC                                                                              2.69                                                         n-pentadecane    1.40                                                         1-pentadecene    0.78                                                         other C.sub.15 HC                                                                              1.61                                                         n-hexadecane     1.44                                                         1-hexadecene     0.59                                                         other C.sub.16 HC                                                                              0.88                                                         n-heptadecane    1.32                                                         1-heptadecene    0.28                                                         other C.sub.17 HC                                                                              0.15                                                         n-octadecane     1.05                                                         1-octadecene     0.03                                                         other C.sub.18 HC                                                                              0.09                                                         n-nonadecane                                                                  1-nonadecene                                                                  other C.sub.19 HC                                                             total            100.00                                                       ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        Mixed plastic fraction                                                        Feed Material C for the steam cracker, obtained from the process              according to the invention and the distillation or extraction unit            for removing the aromatics                                                    Composition       % by wt.!                                                   ______________________________________                                        C.sub.2 HC       0.02                                                         C.sub.3 HC       0.25                                                         n-butane         0.10                                                         1-butene         0.37                                                         other butenes    0.10                                                         i-pentane        0.04                                                         n-pentane        2.54                                                         1-pentene        0.42                                                         other pentenes   0.63                                                         n-hexane         1.00                                                         1-hexene         3.89                                                         other hexenes    1.40                                                         methylcyclopentane                                                                             0.19                                                         methylcyclopentene                                                                             0.21                                                         other C.sub.6 HC 1.53                                                         benzene          5.11                                                         n-heptane        1.42                                                         1-heptene        1.76                                                         methylcyclohexane                                                                              0.09                                                         methylcyclohexene                                                                              0.96                                                         other C.sub.7 HC 1.46                                                         toluene          1.99                                                         n-octane         0.02                                                         1-octene         0.04                                                         ethylcyclohexane 5.70                                                         ethylbenzene     0.09                                                         para-xylene      <0.01                                                        meta-xylene      <0.01                                                        ortho-xylene     0.01                                                         styrene          0.18                                                         other C.sub.8 HC 0.01                                                         n-nonane         0.11                                                         1-nonene         0.06                                                         i-propylbenzene  0.09                                                         n-propylbenzene  0.05                                                         other C.sub.9 HC 3.55                                                         n-decane         1.54                                                         1-decene         0.98                                                         other C.sub.10 HC                                                                              1.01                                                         n-undecane       2.20                                                         1-undecene       2.40                                                         other C.sub.11 HC                                                                              5.90                                                         n-dodecane       2.50                                                         1-dodecene       2.30                                                         other C.sub.12 HC                                                                              6.90                                                         n-tridecane      2.55                                                         1-tridecene      2.67                                                         other C.sub.13 HC                                                                              7.08                                                         n-tetradecane    2.53                                                         1-tetradecene    2.31                                                         other C.sub.14 HC                                                                              4.76                                                         n-pentadecane    2.47                                                         1-pentadecene    1.38                                                         other C.sub.15 HC                                                                              2.85                                                         n-hexadecane     2.52                                                         1-hexadecene     1.04                                                         other C.sub.16 HC                                                                              1.54                                                         n-heptadecane    2.34                                                         1-heptadecene    0.50                                                         other C.sub.17 HC                                                                              0.26                                                         n-octadecane     1.82                                                         1-octadecene     0.05                                                         other C.sub.18 HC                                                                              0.16                                                         n-nonadecane     0.03                                                         1-nonadecene                                                                  other C.sub.19 HC                                                             total            100.00                                                       ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        Mixed plastic fraction                                                        Feed material D = gas mixture for the steam cracker, obtained                 from the process according to the invention                                          Composition                                                                            % by wt.!                                                     ______________________________________                                               H.sub.2 1.32                                                                  CH.sub.4                                                                              8.29                                                                  C.sub.2 H.sub.6                                                                       8.94                                                                  C.sub.2 H.sub.4                                                                       10.40                                                                 C.sub.3 H.sub.8                                                                       6.95                                                                  C.sub.3 H.sub.6                                                                       20.49                                                                 i-C.sub.4 H.sub.10                                                                    0.28                                                                  n-C.sub.4 H.sub.10                                                                    2.25                                                                  l-C.sub.4 H.sub.8                                                                     4.27                                                                  i-C.sub.4 H.sub.8                                                                     6.77                                                                  2-C.sub.4 H.sub.8 t                                                                   1.65                                                                  2-C.sub.4 H.sub.8 c                                                                   2.32                                                                  C.sub.4 H.sub.6                                                                       1.20                                                                  i-C.sub.5 H.sub.12                                                                    0.18                                                                  n-C.sub.5 H.sub.12                                                                    10.62                                                                 C.sub.5 H.sub.10                                                                      7.51                                                                  benzene 1.06                                                                  C.sub.6 H.sub.12                                                                      5.50                                                                  total   100.00                                                         ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        Mixed plastic fraction                                                        Cracked product from the steam cracker with feed material C                   from the process according to the invention                                   Composition     % by wt.!                                                     ______________________________________                                        CO             0.1                                                            H.sub.2        0.8                                                            CH.sub.4       11.1                                                           C.sub.2 H.sub.6                                                                              3.0                                                            C.sub.2 H.sub.4                                                                              27.2                                                           C.sub.2 H.sub.2                                                                              0.4                                                            C.sub.3 H.sub.8                                                                              0.5                                                            C.sub.3 H.sub.6                                                                              13.8                                                           propyne        0.2                                                            propadiene     0.3                                                            i-C.sub.4 H.sub.10                                                                           0                                                              n-C.sub.4 H.sub.10                                                                           0.1                                                            1-butene       1.5                                                            i-butene       1.3                                                            2-butene (c)   0.5                                                            2-butene (t)   0.3                                                            C.sub.4 H.sub.6                                                                              5.8                                                            C.sub.5 HC     4.9                                                            C.sub.6 -C.sub.8 NA                                                                          1.7                                                            benzene        12.2                                                           toluene        5.0                                                            EB + xylenes   1.0                                                            styrene        1.5                                                            C.sub.9 HC     1.2                                                            C.sub.10 + HC  5.5                                                            total          100.0                                                          ______________________________________                                    

                  TABLE 15                                                        ______________________________________                                        Mixed plastic fraction                                                        Cracked product from the steam cracker with feed material D                   from the process according to the invention                                   Composition     % by wt.!                                                     ______________________________________                                        CO             0.2                                                            H.sub.2        1.7                                                            CH.sub.4       19.3                                                           C.sub.2 H.sub.6                                                                              6.7                                                            C.sub.2 H.sub.4                                                                              31.8                                                           C.sub.2 H.sub.2                                                                              0.7                                                            C.sub.3 H.sub.8                                                                              2.1                                                            C.sub.3 H.sub.6                                                                              16.1                                                           propyne        0.4                                                            propadiene     0.6                                                            i-C.sub.4 H.sub.10                                                                           0.1                                                            n-C.sub.4 H.sub.10                                                                           0.3                                                            1-butene       0.9                                                            i-butene       2.0                                                            2-butene (c)   0.4                                                            2-butene (t)   0.3                                                            1,3-C.sub.4 H.sub.6 + VA                                                                     4.5                                                            C.sub.5 HC     2.6                                                            C.sub.6 -C.sub.8 NA                                                                          0.5                                                            benzene        5.1                                                            toluene        1.4                                                            EB + xylenes   0.2                                                            styrene        0.5                                                            C.sub.9 HC     0.2                                                            C.sub.10 + HC  1.5                                                            total          100.0                                                          ______________________________________                                    

We claim:
 1. A process for recycling plastic waste in a steam cracker,wherein a melt obtained from heating plastic waste is converted intosteam cracker feed products by heating the melt at from 400° to 550° C.and a distillate fraction separated from said products at from 180° to280° C. is fed to a steam cracker.
 2. A process as defined in claim 1,whereinthe plastic waste is melted, the melt is fed to a reactor wherethe polymers are converted into products at from 400° to 550° C., adistillate fraction is separated by distillation at from 200° to 280° C.from the products, the other products are returned to the reactor, withthe exception of residues and solids and any inorganic acids, and thedistillate fraction separated off is introduced, optionally afterfurther separation, as a feed material into the steam cracker.
 3. Aprocess as defined in claim 1, wherein the distillate fraction isseparated by distillation from the products by a process in whichtheproducts are separated by means of a 1st column which is directlydownstream of the reactor, and intoa bottom product resulting at from300° to 420° C., which, after removal of the residues and solids, isreturned to the tubular furnace, and into a top product resulting atfrom 200° to 280° C., which, after partial condensation, is fed to a 2ndcolumn at from 70° to 150° C., the liquid/gas mixture resulting afterthe partial condensation is separated by means of the above 2nd columnintoa liquid mixture emerging at the bottom of the 2nd column, which is,in part returned to the 1st column, and, in part, used as feed materialfor the steam cracker, and into a gas mixture emerging at the top of the2nd column, which is used as feed material for the steam cracker.
 4. Aprocess for recycling chlorine-containing and/or aromatics-containingplastic waste in a steam cracker as defined in claim 1, whereintheplastic waste is melted at from 280° to 380° C. with dehydrohalogenationof the chlorine-containing plastic, the melt is fed into a reactor wherethe polymers are converted at from 410° to 530° C. into products, theabove products are separated by means of a 1st column which is directlydownstream of the reactor intoa bottom product resulting at from 330° to450° C., which, after removal of the residues and solids, is returned tothe reactor, and into a top product resulting at from 200° to 280° C.,which, after partial condensation, is fed to a 2nd column at from 70° to150° C., the liquid/gas mixture resulting after the partial condensationis separated by means of the above 2nd column, intoa liquid mixtureemerging at the bottom of the 2nd column, which is, in part, returned tothe 1st column and, in part, fed to a distillation or extraction unitsuitable for removing aromatics, and into a gas mixture emerging at thetop of the 2nd column, which is used as feed material for the steamcracker.
 5. A process as defined in claim 4, wherein the liquid mixturefed to the distillation or extraction unit is separated intoa liquidfraction which is used as feed material for the steam cracker, and intoan aromatic fraction.
 6. A process as defined in claim 1, wherein theplastic waste employed comprises a blow molded fraction consisting ofbottles and containers composed essentially of polyolefins, optionallywith adherent soiling, sticky label materials, fillers and residualcontents.
 7. A process as defined in claim 1, wherein the plastic wastecomprises a mixed plastic fraction composed essentially of polyolefins,polystyrene and polyvinyl chloride, optionally with adherent soiling,sticky label materials, fillers and residual contents.
 8. A process asdefined in claim 1, wherein the plastic waste employed comprises a sheetfraction composed essentially of polyethylene, polypropylene, includingoptional soiling, sticky label materials, filler and residual contents.9. A process as defined in claim 1, wherein the plastic waste employedcomprises a light fraction consisting essentially of polyethylene,polypropylene and polystyrene, including optional soiling, sticky labelmaterials, fillers, residual contents.